The present invention relates to a radiant unit in the form of a plate-like assembly with a supporting frame which accommodates a plurality of radiant lamps on mountings, the radiant lamps being protected by a front cover and a rear cover, while the front cover which is permeable to radiation is removably held.
Such radiant units are generally known, for example from Heraeus Quarzschmelze's product information on INFRAROT "Medium-wave Modular Infrared Radiator", Q-D1/140 D/E, D/E 3c 6.85/VN S&S. These radiant units can be used for drying and heating in the production of small parts in the laboratory and in the molding of thermoplastics. The size of these radiant units amounts to about 250.times.500 mm. Several of radiant units of this kind can be assembled to form a wall or other large-area radiant unit, such as a radiation tunnel or a portal for irradiating large pieces or objects. The housing of these radiant units consists of a sheet metal box open at one end with a supporting frame as reinforcement, from whose open end the radiator is inserted and fastened. Depending on the application, the front side of these radiant units is covered by a grille, for example. Radiant units are also known, however, in which the covering consists of a glass plate which is permeable to the radiation (usually infrared radiators are used in such radiant units). After a relatively long period of use it is found that dust and other dirt particles settle on the covers, which from time to time fall on the object being irradiated, or on the other hand reduce the transparency of a plate. The covers must therefore be cleaned repeatedly or replaced; for this purpose cleats with which they are fastened to the supporting frame have to be removed and then screwed back again. Furthermore, it has been found that covers of vitreous fused silica fastened with cleats break, since when the radiator is in use tensions develop between the glass plates and the frame or covers, due to the different coefficients of longitudinal expansion.